1. Field of the Invention
This invention relates to a chip card with a display, in particular an electronic purse in chip card format, comprising a chip card processor for processing data and a display controller for driving the display to display certain data on the display.
2. Description of the Background Art
Such a chip card is known for example from DE 196 31 557 A1. The display serves the purpose of permitting the data content of the chip card, for example the cash balance of the electronic purse, to be determined without any technical aids by being indicated on the display. The display controller is formed as a chip separate from the chip card processor for security reasons, but can also be implemented physically on the chip of the chip card processor as a logically and functionally separate unit.
However, since a great number of connecting leads must be conducted from the display to the display controller, altogether 35 leads for a five-place 7-segment display, it is inexpedient to implement the display controller on the chip of the chip card processor. Instead, a separate display controller chip is usually integrated into the display and applied to the same glass or plastic substrate on which the display is built up. This is expedient in particular when the display has transparent indium-tin oxide conductive paths (ITO) so that the connecting leads to the display controller can likewise be realized as ITO conductive paths on the same substrate without any special effort.